When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform dependably, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) Sho 60-242038.
According to this publication, this method of pipe repair comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, like air and water. The tubular liner bag is made of a flexible resin-absorbent material impregnated with a thermosetting resin, and has the outer surface covered with an impermeable plastic film.
More particularly, according to the publication, the tubular flexible liner bag is closed at one end and open at the other; the tubular flexible liner bag is first flattened, then, the closed end of the tubular liner bag is tied to a control rope; the open end of the tubular liner bag is made to gape wide and hooked (anchored) at the end of the defective or old pipe in a manner such that the wide-opened end of the liner completely and fixedly covers and closes the pipe end; a portion of the liner is pushed into the pipe; then, the pressurized fluid is applied to the said portion of the tubular liner such that the fluid urges the tubular liner to enter the pipe. Since one end of the tubular liner is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag is turned inside out as it proceeds deeper in the pipe, and this manner of insertion is exactly what is meant by the term "everting" as used above and it shall mean so throughout this application document. When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the control rope holds the closed end of the tubular liner bag to thereby control the length of the tubular liner in the pipe. Then, the everted tubular liner is pressed against the inner wall of the pipe by the said pressurized fluid, and the tubular flexible liner is hardened as the thermosetting resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag by means of a hot steam, etc. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
Now, in this method of underground pipe repair, the pressurized fluid can be anything, but the most frequently used is pressurized water, then compressed air is the next most frequently used, and on many occasions pressurized water and compressed air are used in combination. However, in each of these cases there were certain advantages and disadvantages; for example, the apparatus installed on the ground to effect everting was complicated and large in size.
Accordingly, in order to overcome such disadvantages, the present applicants had proposed a method which introduced a device by virtue of which it became possible to evert the tubular liner bag easily with a compact apparatus much smaller than the conventional apparatus. This method and the device are described in detail in Japanese Provisional Patent Publication (Kokai 5-42485, and will be described here briefly with reference to FIG. 5.
In FIG. 5, the reference numeral 101 designates a tubular liner bag soaked with thermosetting resin, and two closed air bags 102 and 103 are partially attached to the outer surface (before everting) of the liner bag 101.
According to an embodiment of this method, one end of the tubular liner bag 101 is anchored on a tubular brim 106a of a support frame 106, as shown and turned inside the brim 106a a little; next, into the small pocket caused by this turning, water is charged from a water hose 107, whereby the tubular liner bag 101 is everted and enters partially into a manhole 111, which is a vertical entrance to the pipe 110. When the tubular liner bag 101 hits upon the wall of the pipe 110, the head of the bag 101 is turned to that side of the pipe 10 which is to be lined, and the bag 101 is everted into said side of the pipe 110. Then, the air bags 102, 103, which are flattened at the moment, also get into the pipe 110, and, incidentally, the positions at which the air bags 102, 103 are attached to the tubular liner bag 101 are such that when the air bags 102, 103 get into the pipe 110, the air bag 103 stays in the vicinity of the lower end of the manhole 111 and the air bag 102 stays at a location a little farther from the air bag 103, and furthermore, the air bags 102, 103 are attached to the opposite sides of the flattened uneverted tubular liner bag 101, as shown in FIG. 5; so, as the tubular liner bag 101 proceeds into the pipe 110, the air bags 102, 103 enter the pipe 110 and on this occasion the air bags 102, 103 are sandwiched between an everted portion of the tubular liner bag 101 and an uneverted portion thereof. The supply of water is stopped and the liner bag 101 stops everting.
Thereafter, compressed air is supplied from a compressor, not shown, into the air bags 102, 103 via air hoses 104, 105, respectively, whereupon the air bags 102, 103 inflate inside the everted part of the tubular liner bag 101 which has been inserted in the pipe 110, and as the result, the uneverted part of the tubular liner bag 101 is forced to undulate as it runs and describe a locus in a shape of a fallen letter "S", as seen in FIG. 5. Then the supply of water is ceased.
The things being the way they are, compressed air is supplied from a compressor, not shown, via an air hose 108 to dispel some water and form a closed space S filled with compressed air in the head portion of the tubular liner bag 101. As the supply of the compressed air to the closed space S is continued, the closed space S expands, but it does not do so backward, because the water pressure it confronts at the water level formed between the air bags 102 and 103 is greater than the pressure required to force the tubular liner bag 101 to evert. Thus, as the supply of the compressed air is continued, the compressed air does not flow backward and up along the manhole, but causes the tubular liner bag 101 to start everting again prompted by the increased pressure in the closed space S, and thus the tubular liner bag 101 advances in the pipe 110 leftward, as seen in FIG. 5.
As described above, according to this method of everting, the closed space S is formed in the tubular liner bag 101 inserted in the pipe 110, and everting is effected by means of the pressure of the compressed air supplied to this closed space S, so that it is possible to reduce the size of the apparatus for eversion installed on the ground and eversion itself can be conducted with high operation efficiency and ease.
However, in this eversion method, when the air bags 102, 103 are inflated inside the tubular liner bag 101, as shown in FIG. 5, the air bag 102 is forced to float by the buoyancy caused by the water staying in the tubular liner bag 101, and as the result the air bag 102 can be torn apart from the tubular liner bag 101 where it is adhered to the bag 101, and consequently a burst may occur in the tubular liner bag 101.
Also, this eversion method requires that the air bags 102, 103 be attached to the tubular liner bag 101, so that the preparation of tubular liner bag 101 complete with the air bags is complicated and the manufacturing cost is increased.
The present invention was contrived in view of the above problems, and it is, therefore, a principal object of the invention to provide a new method for everting a tubular liner bag which ensures that the tubular liner bag can be manufactured at a low cost and can be everted effectively and easily with a compact everting apparatus.